The invention relates to an electron beam measuring or testing device for stroboscopic measurement or testing of high-frequency, periodic events. Electron beam testing of electron beams is utilized to measure or test in non-contact manner in environments where the use of a contact probe is undesirable due to capacitive loading and accessibility considerations.
High-frequency periodic events can be stroboscopically measured in integrated circuits with an electron probe. Serving as the check or analysis probe is a focused electron beam which is directed at the subject being tested or measured. Due to the interaction between electrons and the solid body, secondary electrons among other things are released which can be employed for imaging an object. These secondary electrons also carry information concerning the electrical potential at the location of incidence. Upon exploitation of the stroboscopic effect, measuring subjects which function with a high nominal frequency can also be quasi-statically imaged to provide a potential contrast. To this end, the measuring subjet to be examined is targeted with cyclically repeating signals and imaged in a scanning electron microscope. The electron beam is only switched on once in each cycle for a brief time, i.e., the measuring subject or specimen is observed only during a specific phase. Thus, the imaging is a snapshot of the rapidly functioning probe. The point in time at which the electron beam is turned on can be selected at random within the cycle. A slow-motion representation of the switching operations is possible by means of slowly shifting the phase. The on-time duration of the electron beam can be reduced down to the picosecond (ps) range, i.e., the chronological resolution of this imaging method lies in the ps range. The electron pulses are generated with the assistance of a beam suppression or blanking system well known to those skilled in this art.
The potential at the point of incidence of the primary electrons is determined with the assistance of a spectrometer from the energy of the secondary electrons which are released in pulse-like fashion. For this purpose, the signal of the secondary electrons which are to pass through the spectrometer are amplified in a scintillator/photomultiplier combination and are further processed after integration in a preamplifier. The arrangement requires:
(1) a phase control with which the phase of the electron pulses is set, and PA1 (2) a preamplifier which can process pulse-shaped signals without overdriving. PA1 (a) A delay generator (Hewlett-Packard) was modified for the phase control. PA1 (b) A special electronics was developed for the drive of the delay generator. PA1 (c) A preamplifier was constructed for the signal processing which, together with a controlled-gain amplifier, makes a potential measurement possible. PA1 (a) The signal processing is insensitive to disruptions of the beam suppression system and is independent of the scanning frequency. PA1 (b) The synchronization ensues automatically. PA1 (c) The signal-to-noise ratio is improved. PA1 (d) Drive of the inventive arrangement via a computer is simplified. PA1 (e) The cost saving amounts to 50%.
Since commercial devices are not available with the required capacity, in electron beam measuring devices for stroboscopic measurement of high-frequency periodic events as previously known, the various components had to be developed (See E. Wolfgang et al, "Electron Beam Testing of VLSI Circuits," IEEE J. of Solid-State Circuits, Vol. SC-14, No. 2, April 1979, pp. 471-481, incorporated herein by reference). In detail, the following components were accordingly constructed:
Despite considerable effort, however, the device does not meet recent demands with respect to capacity, reliability and manipulation.